Really? I actually find them pretty easy, at least on SSE Intense (I haven't tried Boss Battles Intense, though I have no problem with them on Boss Battles Hard). The only attack of Rayquaza that is hard to dodge is when he flys up in the air in a circle and does that lightning thing. The rest are not bad (when he flys across the screen horizontally it can be a bit tricky if you don't time it right though). Sometimes his tail swipe hits me but that doesn't do very much damage at all.
Porky is not hard at all except for when he does his fast side attacks. Everything else is pretty dodgable, though the laser beam can be hard to dodge sometimes (but it doesn't do a ton of damage so it usually doesn't matter).
Honestly I have more trouble with Galleom, mostly because his ground pounding thing is hard to avoid (though it mostly just roots you, only does about 20% dmg) and occassionally he'll decide to face-plant on top of you which is pretty much an insta-kill if you can't avoid it. I usually just use a Heart Container before I fight him though and that's enough to get me through the fight without being launched. Duon is not too bad, except when he gets a cheap shot off. And both Ridleys and both Hands (Master and Crazy) are rediculously, extremely easy.
Honestly, I think even Tabuu would be fine except for the red ring of death attack and his little magical yellow cage. The cage is hard to avoid, but it's pretty much an instant death if you can't. The RRoD I have managed to dodge two of the rings but I always get hit by the third. Maybe I just need more practice. I wish you could practice against specific bosses instead of having to beat all of them to fight him (and I could do SSE but he's much harder there since you get 6 lives so it's not quite the same)